Laser projectors are used to project images onto surfaces. The projected images are used as patterns for manufacturing products such as leather products, roof trusses and aircraft parts and tools.
Laser scanners such as those described in U.S. Pat. No. 5,237,444 have been used to project a pattern onto a cylindrical object surface. A focused laser beam is deflected by the use of two orthogonally placed scanners causing the laser beam to follow a varying optical path to various object points. The scanners each pivotally rotate a mirror which will direct the laser beam to any point on the object's surface. This type of scanner can accept CAD data to project a very accurate image onto the object's surface. However, these scanners are useful only to project an image.
In still other types of scanners as disclosed in U.S. Pat. Nos. 4,797,747, 4,816,920, 5,048,904 and 5,150,249, scanning systems project an image onto a two dimensional surface. These scanners are used for projecting images for laser printers or reading an image from a surface for facsimile image transmission devices. In this type of apparatus, a beam splitter is used to direct a portion of the laser beam to a photo detector or sensor that monitors the beam intensity and provides a corresponding feedback signal to a logic controller or host computer to maintain a constant beam intensity. By using a beam splitter, the laser beam is attenuated resulting in a loss of power which can be as high as 50%.
Still other optical scanners utilize a conventional laser projector with optical sensors mounted on the object itself. When the laser beam contacts the optical sensor, a corresponding signal is generated and sent back to a logic controller. However, this system requires that the optical sensors be wired directly to the logic controller. In many heavy industrial situations, a series of wires is unacceptable for implementation.
These scanning applications begin with the generation of computer aided design (CAD) data. The laser projector interprets the CAD data and projects the pattern onto the surface to be used. For parts designed with CAD or simple parts, a CAD data file is readily available or can be easily generated. However, for complicated products designed without the benefit of a CAD system, the CAD data cannot be easily generated.
This problem is particularly acute in the aircraft industry where many aircraft which are still in service were not designed with the benefit of CAD. All parts, including replacement parts, and tools for making such parts must be manufactured without CAD.
Many of these parts and tools were manufactured by applying a patterned MYLAR sheets onto a surface to be machined. The generation of patterned MYLAR sheets can take up 6-8 weeks to produce. The application of MYLAR sheets to surfaces which are curved in more than one dimension causes the MYLAR sheet to buckle, dramatically decreasing the accuracy of the desired pattern.
For parts and tools which do not have readily available CAD data describing the part or tool, CAD data could be generated either by redesigning the tool or part using CAD or by digitizing the tool or part directly from an existing part. Both solutions pose problems relating to the accuracy of the generation of accurate CAD data.
Several apparatus exist for digitizing parts or tools. A laser beam can be projected at a tool or part. The reflected light is received by video equipment which interpret the received light and the angle of reflectance to triangulate the point of reflectance and fix its point in 3 dimensional space. By repeating the process for different locations on the tool or part CAD data may be generated to facilitate the manufacture of additional parts. However, this process could be time consuming and the degree of accuracy is dependent upon the relative lack of motion. Additionally, a dedicated system must be purchased.
In a commonly assigned United States patent application, Ser. No. 08/212,665, filed Mar. 14, 1994, a laser projector is described. The laser projector uses a wedge-shaped lens having a central aperture. The laser beam is focused through the aperture preventing attenuation of the laser beam. The laser beam is then projected towards a pair of galvanometers which directs the laser beam to a surface in a predetermined pattern. A reflector is used to reflect the laser beam back to its source. Since the return beam is more diffuse or wider than the focused laser beam, the laser beam will be refracted by the wedge-shaped lens to a sensor. On receipt of light, the sensor will generate a feedback signal.
This type of laser projector can place an object in 3D space by using known theories (see Rueb, K.: "Hypothesis Refinement for 3D Scene Interpretation", PhD Thesis, University of Waterloo, 1990). By knowing the dimensions of a number of reflectors on a surface relative to each other, the position of the object relative to the laser projector can be calculated. Once calibrated, the laser projector can project a predetermined image onto a surface using a CAD data file.
Heretofore, such laser projectors have only been used to project an image or pattern onto a surface.